AArch64: C1 StubAssembler::call_RT can corrupt stack

StubAssembler::call_RT() has some code to shuffle arguments using the stack as temporary storage:

  // if there is any conflict use the stack
  if (arg1 == c_rarg2 || arg1 == c_rarg3 ||
      arg2 == c_rarg1 || arg2 == c_rarg3 ||
      arg3 == c_rarg1 || arg3 == c_rarg2) {
    stp(arg3, arg2, Address(pre(sp, 2 * wordSize)));
    stp(arg1, zr, Address(pre(sp, -2 * wordSize)));
    ldp(c_rarg1, zr, Address(post(sp, 2 * wordSize)));
    ldp(c_rarg3, c_rarg2, Address(post(sp, 2 * wordSize)));

Unfortunately there's a typo: the first pre(sp, 2 * wordSize) should be pre(sp, -2 * wordSize) otherwise the pushes and pops are unbalanced.

I think this was exposed by JDK-8259619 which fixed the conflict check but AFAIK it only causes a problem on the Valhalla lworld branch and is not used otherwise.